Manufacture of bitumen pipes

ABSTRACT

A reinforced bitumen pipe has an inner, strength-providing, reinforced thermosetting resin layer which is coated on its inner and outer sides with a bitumen layer. The bitumen layer on the inner side, and preferably also the bitumen layer on the outer side, is separated from the strength-providing reinforced thermosetting resin layer with the aid of an insulating glass fiber layer into which the thermosetting resin and the bitumen partially penetrate without finding their way up to each other.

This application is a division of application Ser. No. 34,884, filed May1, 1979, now U.S. Pat. No. 4,289,172.

The reinforced bitumen pipe is manufactured by first producing a curedthermosetting resin layer with inner and outer insulating glass fiberlayers only partially penetrating into the cured resin layer, whereuponthis semi-finished product after some aging is coated with bitumenlayers internally and externally, said bitumen layers being caused topartially penetrate into the adjoining insulating glass fiber layer. Ina modification of this process the inner bitumen layer is first appliedto a mandrel which has been coated with release agent and then theinsulating glass fiber layer is wound under tension onto the still hotand plastic inner bitumen layer so that the bitumen partially penetratesinto the glass fiber layer. The thermosetting resin layer is thensuccessively built up on the outer side of the glass fiber layer. Aftercuring of the thermosetting resin layer the outer bitumen layer isapplied to the thermosetting resin layer.

When laying for example sewer pipes in the ground use has been made ofpipes of sundry materials such as PVC, polyethylene, asbestos cement,cast iron. Such pipes are usually relatively expensive even though theplastic pipes can be manufactured at relatively competitive prices.However, the plastic pipes suffer from the drawback that they may besubject to cracking and acquire porosity so that such pipes, especiallypolyester pipes, may be dissolved by soil acids etc.

The present invention has for its object to provide a relativelyinexpensive pipe which possesses the favourable properties of theplastic pipes but is devoid of the disadvantages inherent in these pipesas well as other prior art pipes.

To this end, the invention provides a reinforced bitumen pipe which ischaracterized in that it has an insulating glass fiber layer which atits inner side is united with an inner bitumen layer partiallypenetrating into the glass fiber layer, and at its outer side is unitedwith a strength-providing layer of reinforced thermosetting resin whichpartially penetrates into the glass fiber layer without reaching thebitumen layer, said strength-providing layer being coated on its outerside with an outer bitumen layer which is preferably separated from thestrength-providing layer by means of a glass fiber layer into which thestrength-providing layer and the outer bitumen layer partially penetratefrom opposite sides without reaching one another, and the outer bitumenlayer optionally has an outer coating of particulate material attachedto its surface.

In this pipe the glass fiber layer or the two glass fiber layers arepreferably formed by dense woven fabric of glass fiber rovings. Thestrength-providing layer may consist of a reinforced polyester. Theinner and/or the outer bitumen layer is preferably reinforced with aglass fiber layer entirely impregnated with bitumen and preferablyconsisting of a diamond fabric (i.e. an open woven glass fiber fabric).

The invention also relates to a process of manufacturing such areinforced bitumen pipe, in which the pipe is successively built up on amandrel which has been coated with a release layer. Characteristic ofthis process is that warm bitumen composition is spread onto the mandrelhaving the release layer to form an inner bitumen layer onto which aglass fiber layer is applied and which is thus caused to partiallypenetrate into the glass fiber layer without finding its way all throughsaid layer, and that a reinforced layer of thermosetting resin issuccessively built up on the outer side of said glass fiber layer and isthereby caused to partially penetrate thereinto without reaching thebitumen layer, after which the layer of thermosetting resin is cured andcoated after curing with an outer bitumen layer which on its outer sideis preferably coated with a particulate material. It is preferred inthis process, when building up the reinforced layer of thermosettingresin on the outer side of the glass fiber layer, first to apply agel-coat layer, on the outer side of which the layer of thermosettingresin is then successively built up by successive application of resinand reinforcing layers to the necessary strength. The resin is cured.The outer bitumen layer is preferably applied only after a givenpostcuring time has passed in order that the major part of thesubstances which have not participated in the curing reaction shall haveescaped before the application of the outer bitumen layer. Preferably,the outer bitumen layer is caused to enclose also the annular endsurfaces of the pipe so that the glass fiber layer and the layers ofthermosetting resin are entirely enclosed by bitumen.

In a further development of this process it has been found to be moreadvantageous first to manufacture the strength-providing reinforcedlayer of thermosetting resin which is thereby united both on its outerand inner sides with glass fiber layers that only partially penetrateinto the layer of thermosetting resin, after which the bitumen layers onthe inner and outer sides are applied. The present invention thus alsoprovides another process of manufacturing the reinforced bitumen pipeconcerned, and in this process a mandrel is coated with a glass fiberlayer on the outer side of which a reinforced layer of thermosettingresin is then successively built up and thereby caused to partiallypenetrate into the glass fiber layer without finding its way all throughsaid layer, whereupon a further glass fiber layer is optionally causedto partially penetrate into the outer side of the thus produced layer ofthermosetting resin, after which the layer of thermosetting resin iscured and coated after curing with outer and inner bitumen layers whichare caused to partially penetrate into the glass fiber layer and ofwhich the outer bitumen layer on its outer side is preferably coatedwith a particulate material, while the inner side of the inner bitumenlayer is preferably postheated for reduction of its porosity.

The application of the inner bitumen layer in said last-mentionedprocess preferably takes place by centrifugal casting of molten bitumenagainst the inner side of the tubular strength-providing layer ofthermosetting resin. Such an application method brings about a verystrong anchorage of the bitumen layer. The application of the outerbitumen layer can be realized by slowly rotating the pipe in a pot ofmolten bitumen, but the application can also be made by spreading theouter bitumen layer with a doctor blade. Same as in the above describedfirst process according to the invention the bitumen layer may on boththe inner and outer sides of the pipe be reinforced to great advantagewith a glass fiber layer, preferably diamond or openly woven fabric,entirely impregnated with bitumen.

The two bitumen layers or, in the first mentioned case, the outerbitumen layer is preferably applied only after a given postcuring timehas passed after the curing of the layer of thermosetting resin in orderthat the major portion of the substances which have not participated inthe curing reaction shall have escaped before the application of thebitumen. The application of the bitumen involves reheating of the layerof thermosetting resin, which results in an improved curing of the layerof thermosetting resin so that the curing reaction is made complete.

The invention is based on the understanding that bitumen is a substancethat withstands both humic acids and the liquids which are meant to flowin the pipes. The bitumen itself, however, has insufficient strength topermit being shaped into pipes of the requisite solidity, in particularresistance to compression. Attempts aiming at a direct application of alayer of thermosetting resin onto the outer side of the inner bitumenlayer have however failed since the substances making up the stilluncured thermosetting resin migrated into the bitumen and modified theproperties thereof, resulting in a poor adhesion of the layer ofthermosetting resin. Therefore, according to the invention, use is madeof a relatively thick glass fiber layer as an "insulating" and bindinglayer between at least the inner bitumen layer and the layer ofthermosetting resin outside it. Although the same problems are notassociated with the application of the bitumen to the outer side, sincethe application of the outer bitumen layer can be carried out after atime sufficient to permit the major portion of the non-reactedcomponents of the thermosetting resin starting materials to escape, itnevertheless is most advantageous to utilize a thick glass fiber layeras an "insulating" and binding layer also between the layer ofthermosetting resin and the outer bitumen layer. After the layer ofthermosetting resin has been coated with bitumen layers and particulatematerial has optionally been attached to the outer side of the outerbitumen layer there is a obtained a reinforced bitumen pipe whichpresents all the advantages of the bitumen along with the strength ofthe thermosetting resin.

As particulate materials for attaching to the outer side of the outerbitumen layer use can be made of crushed stone material, talcum or thelike.

The invention will be described in greater detail hereinbelow withreference to the accompanying drawing in which:

FIGS. 1 and 2 are cross-sections of two embodiments of the bitumen pipeaccording to the invention.

In an embodiment of the invention a pipe was manufactured in conformitywith FIG. 1. This pipe has an inner bitumen layer 10, an insulatingglass fiber layer 11, a glass fiber reinforced layer of thermosettingresin 12, a further insulating glass fiber layer 13, an outer bitumenlayer 14 and a sand coat 15. As illustrated, the inner and outer bitumenlayers may have a reinforcement 16 which is described in the following.At the manufacture of this pipe use was made of a mandrel having adiameter of 20 cm. The mandrel was first covered with a fabric layer ofwoven glass fiber rovings which was helically coiled onto the mandrel toconstitute the layer 11. The glass fiber roving fabric was densely wovenand had a thickness of 0.7-0.8 mm. Then a layer of polyester-based,styrene-containing gel-coat was applied. The gel-coat was creamy and ofsuch a viscosity that it could not penetrate through the glass fiberfabric. As gel coat use can be made of LAMELLON 2670 which is alow-viscous slightly thixotropic polyester which in liquid state has aviscosity of 3-4 P at 20° C. and which can be composed in such a waythat it will have a gelling time of 5-7 minutes and a curing time of10-20 minutes. On the outer side of the gel-coat layer a laminate ofpolyester layers and glass fiber layers was successively built up untilthe requisite number of glass fiber layers and the requisite strengthhad been obtained. As final glass fiber layer, helically coiled web offabric woven from glass fiber roving was applied. Said fabric web wascaused to only partially penetrate into the still uncured polyesterlayer. The gel-coat layer and the glass fiber reinforced polyester layertogether formed the layer 12 of thermosetting resin. The helicallycoiled web of fabric woven from glass fiber roving formed the layer 13.After that the laminate was cured and after curing it was left lying forsome days so that the styrene in the resin could escape. Then thesemi-finished pipe was withdrawn from the mandrel and passed into acoating machine for coating with bitumen. In the coating machine abitumen layer was spread with a doctor blade on the outer side of thepipe. This bitumen layer formed the layer 14 and was applied in athickness of 2-3 mm. As bitumen use was made of a mixture of two asphalttypes, viz. 70% NYNAS 9330 (KoR melting point 93° C., penetration 30mm/10 at 25° C.) and 30% gilsonit, the asphalt or bitumen mixture havinga KoR melting point of 105°-110° C. and a penetration of 11-30 mm/10 at25° C. At the application the asphalt or bitumen mixture had atemperature of 180° C. The asphalt or bitumen mixture was also caused tocover the end surfaces of the layer of thermosetting resin.

The inner bitumen layer 10 was then applied by centrifugal casting ofthe hot asphalt or bitumen mixture which on this occasion had atemperature of 170° C. In the centrifugal casting operation the pipe wasrotated at a peripheral speed of 6 m/min, and the rotation continued for5 minutes after the molten bitumen layer had been applied. The bitumenwas thereby caused to heavily penetrate into the woven glass fiberrovings adhering to the inner side of the thermosetting resin layer,whereby a strong bond was obtained between the inner bitumen layer andthe thermosetting resin layer.

After the bitumen layers had cooled the inner bitumen layer washeat-treated with the aid of gas flames to partially melt the surface ofthe bitumen layer and ensure that the surface was entirely free ofpores.

In another embodiment of the invention the pipe was manufactured inconformity with FIG. 2. This pipe was built up in the same way as thepipe in FIG. 1, except that the layer 13 was lacking. The same referencenumerals have therefore been utilized. In the manufacturing operationuse was made of a mandrel having a diameter of 20 cm. The mandrel wasfirst covered with a release layer which could withstand heat up toabout 230° C. and which was formed by a polyester film or nylon filmhaving a thickness of 0.10 mm. A bitumen layer 10 having a thickness of2-3 mm was then applied to the outer side of the release layer. Saidbitumen layer was formed by the above-mentioned mixture of 70% NYNAS9330 and 30% gilsonit. At the application the asphalt or bitumen mixturehad a temperature of 180° C. With the inner bitumen layer in a softstate (i.e. molten to semi-molten state) a layer of fabric 11 woven fromglass fiber roving was applied and drawn in by about 30% into thebitumen layer. The glass fiber roving fabric was densely woven and had athickness of 0.7-0.8 mm so that the viscous, molten to semi-moltenbitumen could not penetrate the glass fiber fabric. The bitumen was thenallowed to set (cool for about 5 minutes) to a temperature of below 100°C. A layer of polyester-based, styrene-containing gel-coat, theabove-mentioned product LAMELLON 2670, was applied and on the outer sideof the gel-coat layer there was successively built up a laminate ofpolyester layers and glass fiber layers until the requisite number ofglass fiber layers and the requisite strength had been obtained. Thegel-coat layer and the polyester and glass fiber layers applied to theouter side thereof together formed the layer 12. After that the laminatewas cured and left lying for some days after cooling so that the styrenein the resin could escape. The semi-finished pipe was then withdrawnfrom the mandrel, the release layer being also removed. The outer sideof the semi-finished pipe was coated with a new batch of bitumen to forma layer 14 having a thickness of 2-3 mm and enclosing also the annularend surfaces of the pipe.

In the two embodiments of the invention the outer side of the outerbitumen layer can be coated to advantage with talcum, sand or othermaterial 15 to facilitate handling of the pipe.

The inner as well as the outer bitumen layer 10 and 14, respectively,can in both embodiments optionally be reinforced with a glass fiberfabric of its own, which is entirely impregnated with the bitumen andcan be formed by a diamond or openly woven fabric 16 having a weight of200 g/m². The glass fiber fabric placed between the thermosetting resinlayer and the inner and outer bitumen layers, respectively, and which ispreferably made up of densely woven glass fiber roving, preferably has aweight of 780 g/m², which corresponds to a thickness of about 1.2 mm.

The reinforcing layers in the thermosetting resin layer preferably areat least three in number, in both embodiments, and the thermosettingresin layer is dimensioned according to the intended pressure class ofthe pipes. A pipe having a dimension of 500 mm for 10 kg operatingpressure should thus have for instance 6-7 reinforcing layers in thethermosetting resin layer. As reinforcing layers in the thermosettingresin it is advantageous to use glass fiber fabric which has been formedfrom glass roving and which have a tensile strength of about 325 kg/cm.The fabric can have a weight of 780 g/m² and can be wound as a bandage,i.e. helically along the pipe. The same application method can beutilized for the application of the glass fiber layers serving asseparating and binding layers between the bitumen and thermo settingresin layers. Coiling may be performed under a certain pull in orderthat the glass fiber layer be flattened and caused to partiallypenetrate into the substrate.

The reinforced bitumen pipe according to the invention can be in theform of socket pipes or smooth pipes, but can also be formed as bends,T-pipes and pipes of many other shapes. In these cases use must ofcourse be made of mandrels of corresponding shapes.

What I claim and desire to secure by Letters Patent is:
 1. A process ofmanufacturing a reinforced bitumen pipe comprising the steps of:a.covering a mandrel with an insulating glass fiber layer, b. successivelybuilding up on the outer side of the glass fiber layer a reinforcedthermosetting resin layer and causing said resin layer to partiallypenetrate into the glass fiber layer without finding its way all throughsaid layer, c. curing the thermosetting resin layer, and d. coating itafter curing with outer and inner bitumen layers, which are caused topartially penetrate into the adjoining insulating glass fiber layer. 2.A process as claimed in claim 1 wherein prior to said step b. ofbuilding up the reinforced thermosetting resin layer, the outer side ofthe glass fiber layer closest to the mandrel is coated with a gel-coatlayer.
 3. A process as claimed in claim 1 or 2 wherein said step d. ofapplying the outer bitumen layer takes place only after a givenpost-curing time has passed after the curing of the thermosetting resinlayer.
 4. A process as claimed in claim 1 or 2 wherein said step d.includes applying the outer bitumen layer to enclose also the annularend surfaces of the pipe.
 5. A process as claimed in claim 1 or 2further comprising reinforcing at least one of said bitumen layers witha glass fiber layer, entirely impregnated with bitumen.
 6. A process asclaimed in claim 5 wherein said bitumen-reinforcing glass fiber layer isbuilt up of an openly woven fabric.
 7. A process as claimed in claim 1or 2 wherein the inner bitumen layer is applied by centrifugal casting.8. A process as claimed in claim 1 or 2 further comprising the step ofcoating the outer side of the outer bitumen layer with a particulatematerial.
 9. A process as claimed in claim 1 or 2 further comprisingpost-heating the inner side of the inner bitumen layer to reduce theporosity thereof.
 10. A process of manufacturing a reinforced bitumenpipe comprising the steps of:a. covering a mandrel with an insulatingglass fiber layer, b. successively building up on the outer side of theglass fiber layer a reinforced thermosetting resin layer and causingsaid resin layer to partially penetrate into the glass fiber layerwithout finding its way all through said layer, c. applying a furtherinsulating glass fiber layer to partially penetrate into the outer sideof the thermosetting resin layer, d. curing the thermosetting resinlayer, and e. coating it after curing with outer and inner bitumenlayers, which are caused to partially penetrate into the adjoininginsulating glass fiber layer.
 11. A process as claimed in claim 10,wherein in said step c. of applying the outer insulating glass fiberlayer a web of a fabric densely woven from glass fiber roving ishelically coiled under tension onto the outer side of the still uncured,reinforced thermosetting resin layer.
 12. A process as claimed in claim10 or 11, wherein prior to said step b. of the reinforced thermosettingresin layer, the outer side of the glass fiber layer closest to themandrel is coated with a gel-coat layer.
 13. A process as claimed inclaim 10 or 11 wherein said step e. of applying the outer bitumen layertakes place only after a given post-curing time has passed after thecuring of the thermosetting resin layer.
 14. A process as claimed inclaim 10 or 11, wherein said step e. includes applying the outer bitumenlayer to enclose also the annular end surfaces of the pipe.
 15. Aprocess as claimed in claim 10 or 11, further comprising reinforcing atleast one of said bitumen layers with a glass fiber layer, entirelyimpregnated with bitumen.
 16. A process as claimed in claim 15 whereinsaid bitumen-reinforcing glass fiber layer is built up of an openlywoven fabric.
 17. A process as claimed in claim 10 or 11, wherein theinner bitumen layer is applied by centrifugal casting.
 18. A process asclaimed in claim 10 or 11 further comprising the step of coating theouter side of the outer bitumen layer with a particulate material.
 19. Aprocess as claimed in claim 10 or 11 further comprising post-heating theinner side of the inner bitumen layer to reduce the porosity thereof.20. A process as claimed in claim 11 wherein prior to said step c. ofapplying the outer insulating glass fiber layer, the uncured, reinforcedthermosetting resin layer is coated with a gel-coat layer.
 21. A processof manufacturing a reinforced bitumen pipe, in which the pipe issuccessively built up on a mandrel which has been covered with a releaselayer, comprising the steps ofa. spreading warm bitumen composition onthe mandrel having the release layer to form an inner bitumen layer, b.applying an insulating glass fiber layer to said inner bitumen layercausing said bitumen to partially penetrate into said glass fiber layerwithout finding its way all through said layer, c. successively buildingup a reinforced thermosetting resin layer on the outer side of the fiberlayer and causing it to partially penetrate thereinto without findingits way up to the bitumen layer, d. curing the thermosetting resinlayer, and e. coating said thermosetting resin layer after curing withan outer bitumen layer.
 22. A process as claimed in claim 21 wherein insaid step b. of applying the glass fiber layer, a web of a densely wovenfabric of glass fiber roving is helically coiled under tension onto theouter side of the still hot and plastic bitumen layer.
 23. A process asclaimed in claim 21 or 22, wherein prior to said step c. of building upthe reinforced thermosetting resin layer, the outer side of the glassfiber layer closest to the mandrel is coated with a gel-coat layer. 24.A process as claimed in claim 21 or 22 wherein said step e. of applyingthe outer bitumen layer takes place only after a given post-curing timehas passed after the curing of the thermosetting resin layer.
 25. Aprocess as claimed in claim 21 or 22 wherein said step e. includesapplying the outer bitumen layer to enclose also the annular endsurfaces of the pipe.
 26. A process as claimed in claim 21 or 22 furthercomprising reinforcing at least one of said bitumen layers with a glassfiber layer, entirely impregnated with bitumen.
 27. A process as claimedin claim 26 wherein said bitumen reinforcing glass fiber layer is builtup of an openly woven fabric.
 28. A process as claimed in claim 21 or 22further comprising the step of coating the outer side of the outerbitumen layer with a particulate material.